This project is devoted to the investigation of the functioning of lysosomes. Through study of the lysosomal, cytosolic, and Golgi alpha-D-mannosidase we hope to uncover interrelationships among enzymes of the three cell compartments as well as unique roles of these enzymes. Extensive substrate specificity studies are planned. The role of Golgi mannosidase in glycoprotein biosynthesis is being explored and, in a similar connection, characterization of microsomal alpha-D-glucosidase has been initiated. In addition, experiments with an in vitro Acanthamoeba system for phagolysosome fusion will hopefully permit the identification of membrane and environmental factors which determine the specificity of the fusion among these vacuoles. The information obtained should contribute to our understanding of the intracellular dynamics of the lysosomal system. Recent progress includes the development of a light microscopic assay for fusion, which is much faster than the electron microscopic assay used previously.